1. Field of the Invention
The field of art to which this invention pertains is the separation of sterols from crude tall oil, tall oil pitch or wool fat. Specifically, it relates to the concentration of sterols in the unsaponifiable fraction of crude tall oil and the separation of high purity sterols therefrom by a solid-bed adsorptive separation, which requires a low-acid sterol feed source. A liquid-liquid extraction process can provide a low-acid, sterol-containing feed directly from crude tall oil. The improved adsorption process utilizes magnesium silicate (Florisil) as adsorbent with a desorbent not previously used.
2. Background Information
It is known in the art to separate sterols from tall oil fractions, e.g., pitch, and from wool fat by adsorption and also by liquid-liquid extraction.
U.S. Pat. No. 4,664,807 discloses the method of isolating cholesterol from tall oil pitch, or other sterol containing materials, in an adsorption column packed with alumina, magnesium silicate (Florisil) or silica gel and eluting the cholesterol with a liquid such as heptane-acetone (19:1) (v:v), toluene-acetone (29:1) (v:v), toluene, heptane-n-butyl acetate (5:1) (v:v) or heptane-toluene-acetone (70:1:9) (v:v:v).
Also in Julian U.S. Pat. No. 3,840,570, sterols are obtained in purified form through a series of steps initiated by a solvent extraction of sterol esters from tall oil pitch utilizing an alcohol/hydrocarbon solvent mixture. In the solvent extraction step, the pitch is first dissolved in the solvent mixture and, after the addition of water, separates into an upper hydrocarbon layer which contains nearly acid-free sterol esters and a lower, alcohol-water phase which contain acids, which are then separated mechanically. Saponification of the hydrocarbon layer containing the sterol esters is followed by additional purification steps to recover the concentrated sterols.
Also, as disclosed in Russian Author's Certificate No. 681,043, published Aug. 25, 1979, tall oil and a polar solvent, e.g., dimethylsulfoxide (hereinafter DMSO), dimethylformamide, acetonitrile or dimethylpyrrolidine is fed into the top portion of an extraction column and a non-polar solvent, e.g., hexane is fed into the bottom portion. Unsaponifiable substances are recovered, after phase separation, in the non-polar solvent and fatty acids and resin acids are recovered in the polar solvent. One objective of the authors is to recover a fatty acid fraction in the polar phase (DMSO) having less than 3% unsaponifiables, but sterols are not mentioned nor is the effect of acid in the unsaponifiable fraction. No mention is made of the use of separate input streams for DMSO, crude tall oil feed and hexane with the feed introduced in an intermediate zone in order to obtain a substantial reduction in the acid in the hexane extract phase.
Tall oil contains several sterols, including campesterol, .alpha.- and .beta.-sitosterol, the latter of which is especially used in cosmetics, such as moisturizing cream, lipstick, etc., as an emulsifier, viscosity regulator, emulsion stabilizer, and skin softener. Wool fat contains cholesterol, which has the same uses listed above. Sterols from both sources also have medicinal uses and are useful chemical intermediates.
Crystalline aluminosilicates or zeolites having high physical strength and attrition resistance, are used in adsorption separations of various mixtures in the form of agglomerates. Methods for forming the crystalline powders into such agglomerates include the addition of an inorganic binder, generally a clay, comprising silicon dioxide and aluminum oxide, to the high purity zeolite powder in wet mixture. The blended clay zeolite mixture is extruded into cylindrical type pellets or formed into beads which are subsequently calcined in order to convert the clay to an amorphous binder of considerable mechanical strength. As binders, clays of the kaolin type or silica are generally used. It is also known that water permeable organic polymers are superior binders.
The invention herein can be practiced in fixed or moving adsorbent bed systems by batch or continuous processes, but the preferred system for this separation is a continuous countercurrent simulated moving bed system, such as described in Broughton U.S. Pat. No. 2,985,589, incorporated herein by reference. Cyclic advancement of the input and output streams can be accomplished by a manifolding system, which are also known, e.g., by rotary disc valves shown in U.S. Pat. No. 3,040,777 and 3,422,848. Flow rates in the various zones may be set and regulated by a programmed flow controller. Equipment utilizing these principles are familiar, in sizes ranging from pilot plant scale (deRossett U.S. Pat. No. 3,706,812) to commercial scale with flow rates from a few cc per hour to many thousands of gallons per hour.
The functions and properties of adsorbents and desorbents in the chromatographic separation of liquid components are well-known, but for reference thereto, Zinnen et al. U.S. Pat. No. 4,642,397 is incorporated herein.
It is an object of the present invention to separate sterols, as a class, from any available sterol-containing natural or synthetic materials, thereby obtaining said sterols in greater purity and increased recovery.
An object is to provide an adsorptive separation process for obtaining high purity sterols from various feed sources using a superior adsorbent which is capable of isolating substantially more of the sterols contained in the feed than with the disclosure of a continuous, simulated moving bed adsorption separation process in copending application Ser. No. 131,611, filed Dec. 11, 1987, wherein activated carbon is the adsorbent used; to avoid deactivation of the Florisil adsorbent, however, it is essential that the acid in the feed be no more than about 1%.
It is a further object to provide a dramatically improved desorbent for the chromatographic separation that gives a 250% increase in selectivity compared to prior art desorbents, e.g., toluene.
Another object of this invention is to produce a sterol fraction directly from crude tall oil by a combination of a liquid-liquid extraction process which provides a relatively acid-free sterol fraction and a chromatographic adsorptive process which is most advantageous when a low acid feed is used.
It is a further object to obtain very pure sterols in good yield from tall oil sources without first having to pitch the crude tall oil, a process that includes heating the crude tall oil to high temperatures under vacuum. The pitching treatment reduces the recovery of sterols possible because some of the sterols are dehydrated under those conditions.